Designers of internal combustion engines implement various technologies and control strategies to improve performance parameters, including reducing exhaust emissions, increasing engine power, and improving fuel economy. A technology presenting opportunities for such improvements is in the area of improved valvetrain control, which seeks to improve performance by improving engine breathing and reducing pumping losses, thus improving volumetric efficiency. Improvements in engine performance through use of valvetrain control strategies benefit conventional spark-ignition engines, compression-ignition engines, and engines that employ intermediate engine strategies, such as homogeneous-charge compression-ignition engines.
Valvetrain control strategies can include control of magnitude of valve lift or valve opening, duration of valve opening, and timing of valve opening, and encompass intake valves and/or exhaust valves. A variable cam phasing system typically alters timing of intake valve opening relative to crankshaft position by employing an oil pressure-actuated phasing device that alters only timing of intake or exhaust valve opening without effecting magnitude of valve lift or valve opening duration. A variable lift control system typically alters magnitude and duration of valve opening by employing a two-step cam shaft, wherein each step of the camshaft is selectable. A fully flexible valve actuation system provides variable cam phasing and variable lift control to permit control of valve opening duration, valve lift, and valve timing.
On an engine system employing a valve actuation system, there is a risk of collision between engine valves and pistons. Piston/valve collisions result in unwanted noise and risk of damage to engine components, leading to warranty and costly repairs. Engine designers generally have avoided piston/valve collisions by restricting range of operation of the valve control devices. However, restricting range of operation of a valve control device reduces the ability of the engine designer to optimize engine performance over its range of operation.
Therefore, what is needed is a method and system which permits operation of a variable valve actuation system over its available range operation, while eliminating risk of harm to the engine due to collision between engine valves and pistons. Such a system and method enables a more aggressive valve control strategy to maximize engine performance in various powertrain applications.